Couldn't match type `Id (Id Char)' with `Char'

'foo' is expected to type check given that 'bar' and 'qux' type check.

ghc_bug.hs:21:7:
    Couldn't match type `Id (Id Char)' with `Char'
    Expected type: (:.:) Id Id Char
      Actual type: Char
    In the expression: 'x'
    In an equation for `foo': foo = 'x'

{-# LANGUAGE TypeOperators, TypeFamilies #-}
module Main where

type family (:.:) g f a where
 (:.:) g f a = g (f a)
--

type family Id x where
  Id x = x
--

-- Type checks
bar :: Id (Id Char)
bar = 'x'

-- Type checks
qux = 'x' :: (Id :.: Id) Char

-- Couldn't match type `Id (Id Char)' with `Char'
foo :: (Id :.: Id) Char
foo = 'x'

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import typechecker labels

closed

Same as #9898 I'm afraid. HEAD says

T9897.hs:20:8:
    Type family ‘Id’ should have 1 argument, but has been given none
    In the type signature for ‘foo’: foo :: (Id :.: Id) Char

So I'll close this as a dup of #9898.

Simon

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate

added Pnormal label